5-5

Viewing IP Group Statistics
Setting the Time To Live Option
When a device transmits an IP datagram, it sets the amount of time, in seconds,
the datagram is allowed to exist, by setting the Time-To-Live (TTL) field located in
the datagram’s header. This eliminates the possibility that a datagram could
travel around a network forever. If the TTL timer expires before the datagram
reaches its destination, the datagram is discarded and an error message is
returned to the original sending device.
Each gateway along the datagram’s path from source to destination decrements
the TTL field by 1 when it processes the datagram’s header field. The gateway
also records the local time of datagram arrival and decrements the TTL timer by
the number of seconds the datagram remained in the gateway awaiting service.
To set the Time To Live Option:
1. Click on the I-bar cursor ( ) to the right of the Time To Live text box. The IP
Group Time To Live text box, Figure5-2, opens.
Figure5-2. Time To Live Text Box
2. Enter the new default Time To Live (in seconds) in the text box. The allowable
time values are 0 to 255.
3. Click OK.
The new default Time To Live displays in the text box. This indicates the number
of seconds a datagram can continue to exist on the network. Any datagram that
exceeds this limit will be discarded.